Sweet Corn Pheromone Trap Network

for Western NY - 2010

This is a seasonal scouting report giving growers in the Western New
York area information on the presence of sweet corn pests and recommendations
on scouting and thresholds. The report is written by Abby Seaman, NYS IPM's
Area Extension Educator for Vegetables.

For 7/20/10

European corn borer trap catches increased a substantially this week
at several locations, with high E race catches at a couple of locations
and high Z race catches at a couple of different locations. ECB catches
at most sites remain in the single digits. Corn earworm were caught
at more locations this week, mostly still in the single digits, but numbers
in Hamlin are high enough to call for a 4-day spray interval. The
first fall armyworm moths were caught this week in Bellona. Western
bean cutworm were caught at 10 locations, and where they were caught, numbers
ranged from 1 to 13. The high catch was in again in Eden, Erie county.
At the field corn and dry bean locations last week, WBC catches remain low,
and ranged from 0-4 per trap.

Scouting and threshold information for fresh market sweet corn:
Split field demonstrations have shown that applying insecticides to sweet
corn for worm control before tassel emergence does not produce better results
than waiting until the recommended tassel-emergence spray timing.

In fields still in the whorl stage when eggs are deposited, larvae move
to the whorl, feed on the foliage and un-emerged tassel, and are found feeding
on the tassel when it emerges.

Larvae feeding in the whorl are protected from insecticide applications
and mortality will not be as high as at tassel emergence, when larvae feeding
in the emerging tassel are exposed to the spray. Fields should be first
scouted for ECB and FAW larvae at early tassel emergence. For corn
borers, look down into emerging tassels for tiny larvae or frass (white
to brown material about the size of fine sand), holes through the leaves
in straight lines, or "windowpaning" damage, in which tiny larvae leave
the clear lower epidermis of the leaf intact as they feed. For armyworms
look for ragged feeding holes and frass pellets the texture of coarse sawdust.

The threshold at tassel emergence is 15% infested plants.
Before any insecticides have been applied, scouting is fast and easy because
any sign of feeding is an almost sure sign of live larvae, so it's not necessary
to spend time finding the larvae. After the initial insecticide application,
feeding damage may be from a larva that has already been killed, so finding
the critter is more important for an accurate estimate of the number of
infested plants.

Larvae will leave the tassel as it opens up and no longer provides a
moist, protected feeding environment, and move down the plant looking for
protected places to feed. Insecticide applications need to be timed
to kill larvae before they bore into a new feeding location where they will
be again protected from sprays. In fields with very uneven development,
two applications may be necessary, one when approximately 25-50% if the
tassels have emerged, and again after 75-100% of the tassels have emerged,
if the field is still over threshold.

Once a field reaches the silk stage, the threshold drops to 5% infested
plants. Scout the ear zone (roughly from two leaves above and one leaf below
the ears) for ECB egg masses and ECB larvae. Egg masses are found
most frequently on the underside of leaves near the midrib, and consist
of approximately 10-20 flattened eggs overlapping like fish scales. Eggs
are white when first laid, turning cream colored after a couple of days,
and show the black head capsules of the tiny larvae through the surface
of the eggs when within 1 day of hatching (the "black head" stage).
Egg masses can also sometimes be found on the flag leaves of the ears or
on the husk itself. Eggs take approximately 100 base 50 degree days
to hatch. When temperatures are in the 70's during the day and
the 50's at night egg masses will take about a week to hatch. When
temperatures are in the 80's during the day and the 60's at night, they
could hatch in only 4 days.
Look down into the tops of the silks for newly hatched larvae, and pull
the ear away from the stalk slightly to look for larvae feeding between
the stalk and the ear.

Once CEW are being caught in higher numbers, insecticide applications
in silk stage fields should be determined by CEW trap catches. The
recommended spray intervals for CEW should be adequate for ECB and FAW control.
Because CEW lay their eggs directly on the silk, and eggs are difficult
to find in the field unless the population is VERY high, we rely on pheromone
trap catches rather than scouting to make CEW management decisions.
It is most important to adhere to the recommended spray intervals when the
field is in the green silk stage. The chart below indicates recommended
spray intervals during the silk stage for a range of trap catches:

Per Day

Per Five Days

Per Week

Days Between Sprays

<0.2

<1.0

<1.4

No Spray (for CEW)

0.2-0.5

1.0-2.5

1.4-3.5

6 days

0.5-1.0

2.5-5.0

3.5-7.0

5 days

1-13

5-65

7-91

4 days

over 13

over 65

over 91

3 days

Add one day to the recommended spray interval if daily maximum temperatures
are less than 80° F for the previous 2-3 days.

Location

ECB-E

ECB-Z

CEW

FAW

WBC

Avoca (Steuben Co.)

0

0

NA

NA

0

Avon (Livingston Co.)

2

3

2

NA

3

Baldwinsville (Onondaga Co.)

6

4

0

NA

0

Batavia (Genesee Co.)

0

7

0

NA

2

Bellona (Yates Co.)

10

28

NA

2

4

Eden Z (Erie Co.)

0

0

3

0

13

Farmington (Ontario Co.)

0

12

0

0

0

Great Valley (Cattaraugus Co.)

1

2

0

0

1

Hamlin (Monroe Co.)

6

5

14

0

0

Kennedy (Chautauqua Co.)

0

0

3

0

0

King Ferry (Cayuga Co.)

16

0

0

0

0

Kirkville (Madison Co.)

43

4

NA

NA

1

LeRoy (Genesee Co.)

0

0

0

NA

0

Lockport (Niagara Co.)

0

0

3

0

3

Medina (Orleans Co.)

0

0

0

NA

0

Owego (Tioga Co.)

1

11

1

NA

NA

Penn Yan (Yates Co.)

0

17

1

0

3

Pike (Wyoming Co.)

1

5

0

0

0

Plessis (Jefferson Co.)

0

12

0

NA

1

Preble (Cortland Co.)

2

0

0

0

NA

Sherwood (Cayuga Co.)

67

8

0

0

0

Spencerport (Monroe Co.)

0

0

3

0

3

Williamson (Wayne Co.)

0

0

0

0

0

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These pages are maintained by the New York State IPM Program, part of Cornell Cooperative Extension. All material is protected by Section 107 of the 1976 copyright law. Copyright is held by Cornell University and the New York State IPM Program.